| ECG-QT interval
| Brugada Syndrome
| Long QT syndrome (LQTS) Acquired
| Long QT syndrome (LQTS) Congenital
| Torsades de Pointes
| Ventricular Fibrillation
| Ventricular Tachycardia
| Resuscitation - Adult Tachycardia Algorithm
| Automatic Implantable Cardioverter Defibrillator (AICD)
Consider the diagnosis in any patient with polymorphic VT or syncope and focus on drugs and electrolytes as causes. Torsade may be due to inhibition of the HERG type potassium channel. QT prolongation is considered when the QTc interval is greater than 440 ms, but arrhythmias are most often associated with values of 500 ms or more.
- Over 50 known drugs lengthen the QT and this is increasing
- Arrhythmias are associated with prolongation of the QT interval
- Risk of VT, syncope, cardiac arrest, sudden death.
- QT is a period of Ventricular repolarisation and If prolonged acts as a substrate for arrhythmias
- Can lead to polymorphic VT (Torsades de pointes) and VF
- There may be a subclinical genetic predisposition either in cardiac tissue or in the metabolism of particular drugs
- Risk groups include elderly and women (testosterone shortens QTc)
- Those with cardiac and psychiatric disease
- Low magnesium, Low potassium, Low calcium
- Cardiac disorders - chronic heart failure, acute and chronic heart disease, and cardiomyopathies
- Bradycardia due to sinus dysfunction, as well as conduction
- Metabolic, nutritional, neurological and endocrine causes
- Drug-induced LQTS is usually caused by medications that block a cardiac potassium channel in the heart known as HERG or IKr
Drugs that may lengthen QTs (not comprehensive so check BNF)
- Look for antihistamines, antibiotics, antipsychotics and cisapride
- Terfenadine, Astemizole, IV Erythromycin, Clarithromycin, Phenytoin, Lithium,
- Chlorpheniramine, IV Prochlorperazine, Tricyclic antidepressants, Phenothiazine, Halofantrine
- Erythromycin, Phenothiazine, Sotalol, Amiodarone, Class 1a antiarrhythmic drugs, Tricyclic antidepressants, Chloroquine
- Miscellaneous - Acute MI, Starvation, Bradycardia, Myocarditis and HCM, Hypothermia, RV dysplasia.
- Commoner in women
- Asymptomatic, syncope, cardiac arrest, sudden death
- Symptoms may be with exertion and also at rest
- Always ask about a Family history of SCD important
- Take a drug history
- U&E, Magnesium, Calcium
- ECG - Long QTc: Normally, the QTc interval varies from 0.35 to 0.46 seconds (350-460 milliseconds). About 95% of people have a value between 0.38 and 0.44 seconds, which is the range doctors generally consider normal.
- ECG - VF or Torsades de pointes (polymorphic VT)
- Torsades: IV Mg is the agent of choice for immediate treatment of torsade de pointes irrespective of the serum magnesium level. 2g bolus of magnesium sulfate is followed by intravenous infusion of magnesium
- Identify and manage causes when QT prolonged
- Monitor those with a QT > 500 msec and get a cardiology consult
- Do not use Amiodarone or other antiarrhythmics if possible - can make it worse
- Stop any drugs which may be to blame.
- Check and Correct K and Mg
- IV Magnesium can be used. IV Lidocaine can also be used (1)
- Overdrive pacing or just simple pacing if patient's VT is bradycardia dependent and prevents long RR intervals which can predispose to arrhythmias. Isoprenaline has also been used to speed up the heart rate.
- Defibrillation is the treatment of all unstable tachyarrhythmias